During the eleventh to fourteenth centuries, Armenia was subjected to a number of attacks and invasions by Turco-Mongol peoples. The most important of these were the invasions of the Seljuks in the second half of the eleventh century, of the Khwarazmians (1225-1230), and of the Mongols (1223-1247). At the end of the fourteenth century, an already exhausted Armenia was devastated again by the Turco-Mongol armies of Timur-Leng. This study examines the important changes which took place among the Armenians during these four centuries in the history of Asia Minor, the Caucasus, and Cilicia: demographic, economic, and sociopolitical. This article was published as Chapter 10 in The Armenian People from Ancient to Modern Times Vol.1 Richard G. Hovannisian, ed. (New York, 1997) pp. 241-271. Zipped HTML files or pdf available.